Anterior cervical plating system and method

ABSTRACT

The present invention is directed to a system for anterior fixation of the spine that utilizes an elongated fixation plate. The plating system stabilizes the spine and promotes fusion and incorporation of a graft or implant in a portion of the spinal column. In one aspect of the invention, the fixation plate has a first end with a pair of holes. Bone screws extend through the holes to rigidly secure the plate to a first vertebra. The second end of the plate is provided with a pair of slots through which bone screws extend for engagement with a second vertebra. The screws extending through the slots are translatable in the slot to maintain compression of the spinal column portion. The plating system includes a retainer assembly that prevents screw back out. Methods and instruments relating to the plating system are also described.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to the field ofinstrumentation and systems for the spine, and more particularly toinstrumentation and systems for use in treatment of various pathologiesof the cervical spine.

[0002] As with any bony structure, the spine is subject to variouspathologies that compromise its load bearing and support capabilities.Such pathologies of the spine include, for example, degenerativediseases, the effects of tumors and, of course, fractures anddislocations attributable to physical trauma. Spinal surgeons haveaddressed these problems using a wide variety of instrumentation in abroad range of surgical techniques. The use of elongated rigid plateshas been helpful in the stabilization and fixation of the lower spine,most particularly in the thoracic and lumbar spine. These same platingtechniques have found some level of acceptance by surgeons specializingin the treatment of the cervical spine.

[0003] The cervical spine can be approached either anteriorly orposteriorly, depending upon the spinal disorder or pathology to betreated. Many well-known surgical exposure and fusion techniques of thecervical spine are described in the publication entitled SpinalInstrumentation, edited by Drs. Howard An and Jerome Coter. This textalso describes instrumentation that has been developed in recent yearsfor the cervical spine. Plating systems have become predominant forproviding internal instrumentation in techniques that achieve fusion ofthe cervical spinal from an anterior approach.

[0004] During the development of cervical plating systems, particularlyfor the anterior approach, various needs have been recognized. Forexample, the system should provide strong mechanical fixation that cancontrol movement of each vertebral segment. The system should be able towithstand axial loading and continuity with each of the three columns ofthe spine. The system should also be able to maintain stress levelsbelow the endurance limits of the plate material, while at the same timeexceeding the strength of the anatomic structures or vertebrae to whichthe plating system is engaged. The thickness of the system should besmall to lower its prominence, particularly at the smaller spaces of thecervical spine. Also, the screws used to connect the plate to thevertebrae must not loosen over time or back out from the plate.

[0005] While the plating system should satisfy certain mechanicalrequirements, the system should also satisfy certain anatomic andsurgical considerations. For example, the cervical plating system shouldminimize the intrusion into the patient and reduce the trauma to thesurrounding soft tissue. This is particularly important in suchprocedures that relate to the cervical spine because the complicationscan be very devastating, such as injury to the brain stem, spinal cord,or vertebral arteries. It has also been found that the optimum platingsystem permits placement of more than one screw in each of theinstrumented vertebrae. Also, the system should be designed to contactthe vertebrae for greater stability.

[0006] Many spinal plating systems have been developed in the lastcouple of decades to address some of the needs and requirements forcervical fixation systems. However, even with the more refined platingsystem designs, there still remains a need for a system that effectivelyaddresses the requirements for such a system.

[0007] There is also a need for a plating system that addressesprocedures designed to achieve fusion of the cervical spine. In caseswhere a graft or implant is implanted to maintain a disc space and/orreplace one or more diseased vertebral bodies, it is desirable toincrease the rate of fusion and incorporation of the graft or implantinto the spine. A plating system that allows pre-loading of the graft orimplant and/or provides continual loading thereafter is preferred.

[0008] While the prior art plating systems relating to cervical platingsystems are steps in the right direction, there remains a need foradditional improvements. The present invention is directed to satisfyingthese needs, among others.

SUMMARY OF THE INVENTION

[0009] The present invention contemplates a system for anterior fixationof the spine that utilizes an elongated fixation plate. In one aspect ofthe invention, the plating system promotes fusion and incorporation of agraft or implant in a spinal column portion. The plating system providescontinual loading of the graft or interbody implant. In another aspect,the plating system allows a compressive load to be applied to the spinalcolumn portion. This preloading and continual loading avoidsstress-shielding and promotes fusion and incorporation of the graft orimplant into the spinal column portion.

[0010] In one aspect of the invention, the fixation plate has a firstend with a pair of holes. Bone engaging fasteners extend through theholes to rigidly secure the plate to a first vertebra. A second end ofthe plate is provided with a pair of slots through which bone engagingfasteners extend for engagement with a second vertebra. The boneengaging fasteners extending through the slots are translatable in theslots to allow settlement and compression of the second vertebra withrespect to the first vertebra. In a preferred embodiment, the platingsystem includes a retainer assembly that prevents fastener back out.

[0011] According to another aspect of the invention, a bone fixationsystem for a spinal column segment is provided. The bone fixation systemincludes a plate with a central axis, a length between a first end and asecond end, and top and bottom surfaces. The plate defines a pluralityof first openings and a plurality of second openings between the top andbottom surfaces. At least one of the plurality of first openings ispositioned adjacent the first end of the plate and defines a circularhole though the plate. At least one of the plurality of second openingsis positioned adjacent the second end of the plate and defines a slottedhole having a first width and a first length adjacent the bottomsurface. A number of bone engaging fasteners extend through the firstand second openings. Each bone engaging fastener has a threaded shankand an enlarged head. The fastener has a substantially cylindricalportion with a third diameter that interfaces with the plate in thefirst opening such that the fastener inserted in the first openingassumes a fixed orientation with the plate. The head of said boneengaging fastener inserted into the second opening is translatable alongthe length of the second opening to maintain compression of the spinalcolumn portion.

[0012] In another aspect of the invention, a bone fixation system for aspinal column portion is provided. The bone fixation system includes aplate with a length along a central axis that extends between a firstend and a second end. The plate has a top surface and a bottom surfaceand defines a plurality of first and second openings between thesurfaces. At least a pair of the first openings is positioned adjacentthe first end, and the first openings define a circular opening having afirst diameter. At least a pair of the second openings is positionedadjacent the second end, and the second openings define a slot having afirst width and a first length. A number of bone engaging fasteners withan elongated threaded shank and an enlarged head are provided. The boneengaging fasteners extend through the first and second holes from thetop surface. A retainer assembly retains the bone engaging fasteners inthe first and second openings. In one form, the retainer assemblyincludes a washer having a length that substantially corresponds to thelength of the plate.

[0013] In yet another aspect of the invention, a bone fixation systemfor a spinal column segment is provided. The system includes four boneengaging fasteners that have an enlarged head and a threaded shank. Anelongated plate has a length extending between a first end and a secondend sized to span between at least two vertebrae. The plate defines onepair of holes adjacent the first end and one pair of slots adjacent thesecond end. Each of the holes and the slots are configured to receivethe threaded shank of a corresponding one of the bone engaging fastenerstherethrough to engage the plate to the vertebrae. The bone engagingfasteners extend through the pair of holes to fix the plate to the firstvertebra. Bone engaging fasteners extend through the pair of slots tosecure the plate to the second vertebra. The bone engaging fastenersaxially translate in the slots to maintain compression on the spinalcolumn portion.

[0014] In a further aspect of the invention, a bone fixation system fora spinal column portion is provided. The system includes six boneengaging fasteners that each have an enlarged head and a threaded shank.An elongated plate extending between a first end and a second end has alength sized to span between at least three vertebrae. The plate definesone pair of holes over a first vertebra, one pair of slots over a secondvertebra, and one pair of intermediate slots over a third vertebraintermediate the first and second vertebrae. The holes and the slots areconfigured to receive the threaded shank of the bone engaging fastenerstherethrough. The bone engaging fasteners extend through the pair ofholes to fix the plate to the first vertebra The bone engaging fastenersextend through the slots to secure the plate to the second vertebra. Thebone engaging fasteners axially translate in the slots to maintaincompression on the spinal column portion. The surgeon can optionallyplace bone engaging fasteners in the intermediate slots to engage theplate to the third vertebra.

[0015] In another aspect of the invention, there is provided a retainerassembly for an elongated plate that extends between at least twovertebrae. The retainer assembly includes a washer having at least onetapered aperture. The washer is translatable between a locked positionand an unlocked position by threading a locking fastener into thetapered aperture.

[0016] In another aspect of the invention, there is provided a retainerassembly for an elongated plate that extends between at least twovertebrae. The plate defines a number of openings for insertion of boneengaging fasteners to attach the plate to the at least two vertebrae.The plate further includes a first fastener bore in the plate adjacentat least one of the openings positioned over the first vertebra and asecond fastener bore in the plate adjacent at least one of the openingspositioned the second vertebra The retainer assembly includes a washerthat defines at least a first aperture adjacent the at least one openingpositioned over the first vertebra and a second aperture adjacent the atleast one opening positioned over the second vertebra. A lockingfastener for each of the apertures in the washer has an elongated shankextending through the aperture configured to engage the fastener bore ofthe plate. The washer is movable between a first position where the boneengaging fasteners are insertable into each of the at least one openingsand a second position where the washer has a surface configured tocontact the head of a bone engaging fastener extending through the atleast one opening positioned over the first vertebra and overlap thehead of a bone engaging fastener extending through the at least oneopening positioned over the second vertebra.

[0017] In another aspect of the invention, a retainer assembly for anelongated plate is provided. The plate extends between at least twovertebrae and defines a number of openings for insertion of boneengaging fasteners to secure the plate to the at least two vertebrae.The plate includes at least one first fastener bore. The retainerassembly includes a washer that defines at least a first aperturepositioned in communication with the at least one fastener bore. Alocking fastener extends through the first aperture and has an elongatedshank to engage the fastener bore of the plate. The washer is movablealong its central axis between a first position where the at least twobone engaging fasteners are inserted through the openings to engage thefirst and second vertebrae and a second position where a surface of thewasher contacts at least the head of the bone engaging fasteners engagedto the first vertebra.

[0018] In another aspect of the present invention, a method for applyinga compressive load to a number of vertebrae including at least a firstvertebra and a second vertebra is provided. The method includes: (a)providing a template having a guide surface and a notch; (b) positioningthe template on the second vertebra with the guide surface on anendplate of the second vertebra to locate the template notch on the bodyof the second vertebra; (c) inserting a pin through the notch of thetemplate into the body of the second vertebra; (d) removing thetemplate; (e) placing a sleeve over the pin; (f) providing a platehaving a length extending between a first end and a second end, theplate including a notch on the second end and a number of openingstherethrough; (g) placing the plate on the vertebral segment with thesleeve nested in the notch of the plate; (h) fixing the first end of theplate to the first vertebra with bone engaging fasteners extendingthrough the openings positioned over the first vertebra; (i) removingthe sleeve from the pin to form a gap between the pin and the notch inthe plate; (j) connecting a compression tool to the pin and the plate;and (k) applying a compression load to the vertebral segment with thecompression tool until the pin contacts the notch. In one embodiment,the plate includes holes positioned over the first vertebra and slotspositioned over the second vertebra. In another embodiment, the methodfurther includes the step of retaining the bone engaging fasteners inthe plate with a retainer assembly.

[0019] In another aspect of the present invention, there is provided amethod for maintaining compression of a spinal column portion. Themethod includes: (a) providing a plate having a length between a firstend and a second end sized to span at least two vertebra, the platehaving a pair of holes at the first end positioned over the fistvertebra and a pair of slots at the second end positioned over thesecond vertebra; (b) fixing the first end of the plate to the firstvertebra with bone engaging fasteners extending through the pair ofholes; (c) securing the second end of the plate to the second plate withbone engaging fasteners extending through the pair of slots; and (d)translating the bone engaging fasteners in the slots to allow settlingof the spinal column segment. In one embodiment, the method furtherincludes retaining the bone engaging fasteners in the plate with aretainer assembly.

[0020] These and other forms, embodiments, aspects, features, objects ofthe present invention will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a top perspective view of an anterior plating systemaccording to the present invention.

[0022]FIG. 2 is a top perspective view of the anterior plating system ofFIG. 1 with the bone screws locked in place.

[0023]FIG. 3 is a top perspective view of the anterior plating system ofFIG. 1 with bone screws translated in a slot of the plate.

[0024] FIGS. 4(a)-4(f) are top plan views of fixation plates of thepresent invention provided in different sizes and configurations.

[0025] FIGS. 5(a)-5(f) are top plan views of washers of the presentinvention provided in sizes and configurations corresponding to theplates in FIGS. 5(a)-5(f).

[0026]FIG. 6 is a side elevational view of a bone screw according to oneaspect of the present invention.

[0027]FIG. 7 is a side elevational view of a locking fastener accordingto another aspect of the present invention.

[0028] FIGS. 8(a)-8(k) are various views and sections of washersaccording to the present invention.

[0029]FIG. 9 is a top plan view of a first end of the fixation plate ofthe present invention.

[0030]FIG. 10 is a cross-sectional view taken through line 10-10 of FIG.9.

[0031]FIG. 11 is an end elevational view of the plate of FIG. 9.

[0032]FIG. 12 is a top plan view of a second end of the fixation plateof the present invention.

[0033]FIG. 13 is a cross-sectional view taken along line 13-13 of FIG.12.

[0034]FIG. 14 is an enlarged cross-sectional view taken through line14-14 of FIG. 12.

[0035]FIG. 15 is a top plan view of an intermediate portion of thefixation plate of the present invention.

[0036]FIG. 16 is a cross-sectional view taken through line 16-16 of FIG.15.

[0037]FIG. 17 is an enlarged cross-sectional view taken through line17-17 of FIG. 15.

[0038]FIG. 18 is an enlarged cross-sectional view taken through line18-18 of FIG. 15.

[0039]FIG. 19a is a partial sectional view of the anterior plateassembly of the present invention with the screws disposed through theholes at the first end of the plate and engaged in a vertebra.

[0040]FIG. 19b is a partial sectional view of the anterior plateassembly of the present invention with the screws disposed through theslots of the plate and engaged in a vertebra.

[0041] FIGS. 20(a)-20(f) illustrate various instruments and steps of amethod according to another aspect to the present invention.

[0042] FIGS. 21(a)-21 (c) are various perspective views of a compressiontool according to yet another aspect of the present invention.

[0043] FIGS. 22(a)-22(b) are side elevational views of the arms of analternate embodiment compression tool.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentsillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended. Any alterations andfurther modifications in the illustrated devices, and any furtherapplications of the principles of the invention as illustrated herein,are contemplated as would normally occur to one skilled in the art towhich the invention relates.

[0045] A plating system 30 having application in an anterior approach tothe cervical spine is depicted in FIGS. 1-3. The portion of the spine isshown schematically in FIG. 1 to include a first vertebra V1, a secondvertebra V2, and intermediate vertebrae V3 and V4. Preferably, firstvertebra V1 is the inferior or bottom vertebra in the portion of thespinal column and the second vertebra V2 is the superior or top vertebraof the portion of the spinal column. However, it is also contemplatedherein that first vertebra V1 is the superior vertebra and that secondvertebrae V2 is the inferior vertebra. It should also be understood thatas described below, the present invention has application with spinalcolumn portions that include vertebrae ranging in number from two to sixvertebrae. One or more implants I may be placed into one or more of thedisc spaces between adjacent vertebrae as needed. Implant I may be abone graft, fusion device, or any other type of interbody device that isinsertable into a disc space and promotes fusion between adjacentvertebrae.

[0046] In accordance with the present invention, the plating system 30includes an elongated plate 31 having a number of openings therethroughand a number of bone engaging fasteners, shown in the form of bonescrews 50, that are insertable through the openings. In a preferredform, each bone engaging fastener is in the form of a bone screw. Plate31 has a longitudinal axis L extending along the length of the plate atits centerline. Bone engaging fasteners or bone screws 50 are held inplate 31 by way of a retainer assembly 33 positioned along axis L. Theopenings of elongated plate 31 include a pair of holes 34 at first node36 adjacent a first end of plate 31. First node 36 is positioned overfirst vertebra V1. Plate 31 also includes a pair of slots 35 at a secondnode 37 adjacent a second end of plate 31. Second node 37 is positionedover second vertebra V2. In some forms of plate 31, several intermediatenodes 38 are provided along the length of the plate 31 between firstnode 36 and second node 37. Each intermediate node 38 includes a pair ofintermediate slots 32 positioned over a corresponding one of theintermediate vertebrae V3 and V4. Plating system 30 can be fabricatedfrom any type of biocompatible material.

[0047] It is preferred that holes 34 are paired with one of the holes ofthe pair on one side of the longitudinal axis L and the other hole ofthe pair on the opposite side of axis L. Slots 32 and 35 are similarlyarranged in pairs. It is also preferred that paired holes 34 areidentical in shape and size, and are located symmetrically about theaxis L. Paired slots 35 are also identical in shape and size, and arelocated symmetrically about the axis L. The paired slots 32 atintermediate nodes 38 are also identical in shape and size, and arelocated symmetrically about the axis L. Plate 31 includes recessesbetween each of nodes 36, 37, 38 to reduce the outer contouring size ofthe plate. In addition, the recesses between each of the nodes providesan area of reduced material, allowing additional bending of the plate bythe surgeon as may be required by the spinal anatomy. Plate 31 has alength selected by the surgeon with nodes 36, 37, and, if needed, nodes38 to register with the patient vertebrae.

[0048] Plate 31 preferably includes a rounded upper surface 41 that isin contact with the soft tissue surrounding the spine when the plate isengaged to the spine. Rounded surface 41 reduces the amount of traumathat would be experienced by the surrounding soft tissue. The bottomsurface 42 of plate 31 is preferably configured to contact the vertebralbodies of the spine at each of the instrumented levels. In oneembodiment, at least a portion of bottom surface 42 can be texturedalong the length of the plate to enhance its grip on a vertebral body.

[0049] Holes 34 include a recess 45 adjacent the top surface of plate 31that allow the head of the bone engaging fastener, such as bone screw50, to be countersunk in plate 31. Similarly, intermediate slots 32include a recess 46 around each slot 32 adjacent top surface of theplate, and slots 35 include a recess 47 around each slot 35 adjacent thetop surface of the plate. Preferably, slots 35 include a ramp 60 that,as described further below, allows a dynamic compression load to beapplied to the spinal column portion upon insertion of screw 50 atsecond end 43 of slot 35. Recesses 46, 47 also allow the head of screw50 to be countersunk in plate 31 when inserted through a correspondingone of the slots 32, 35. A groove 39 extends along axis L of plate 31and intersects with each of recesses 45, 46, 47 along the length ofgroove 39. The end of plate 31 at second node 37 includes a notch 40,which is preferably rounded with a radius R4 centered on axis L (FIG.12.)

[0050] Retainer assembly 33 includes a washer 90 having a length thatsubstantially corresponds to the length of plate 31. Washer 90 defines aplurality of apertures 91. Each aperture 91 is provided at a bodyportion 93, 94, 95 that corresponds to vertebral nodes 36, 37,38,respectively. A connecting portion 98 extends between and connects bodyportions 93, 94, 95. Each of the apertures 91 has a countersink 92extending therearound adjacent to the top surface of washer 90. Asdescribed more fully below, countersink 92 is tapered from a first widthat the first end of aperture 91 to a second width at the second end ofaperture 91, the first width being greater than the second width.Locking fasteners, shown in the form of screws 85, are positionable,each through a corresponding one of the apertures 91, to engage afastener bore 70 (see FIGS. 4(a)-4(f)) in plate 31 and couple washer 90to plate 31.

[0051] Consequently, retainer assembly 33 retains screws 50 placed intothe vertebral bodies at each of the instrumented levels. Washer 90 istranslatable from an unlocked position (FIG. 1) for bone screw insertionto a locked position (FIG. 2) after screw insertion to contact the headof the bone screws in holes 34 and overlap the heads of bone screws inslots 32, 35. Preferably, washer 90 does not contact the heads of bonescrews in slots 32, 35, thus allowing translation of the bone screws inthe slots. Back-out of the bone screws in slots 32, 35 is prevented whenthe bone screw backs out from its seated position a sufficient amount tocontact washer 90. Preferably, washer 90 resides almost entirely withingroove 39 of plate 31 to minimize the overall height of the construct.

[0052] As shown in FIG. 1, retainer assembly 33 is in an unlockedcondition with screws 85 at the second end of apertures 90. In theunlocked condition, body portions 93, 94, 95 of washer 90 do not overlapholes 34 and a portion of slots 32, 35, and enable insertion of the bonescrews 50 therein. Narrowed portions 98 of washer 90 allow bone screws50 to be placed through holes 34 and slots 35 to secure plate 31 to thevertebrae V1 and V2. If desired, the surgeon can also place bone screws50 in intermediate slots 32 to secure plate 31 to vertebrae V3 and V4 asdeemed necessary. Plate 31 and bone screws 50 preferably interface inholes 34 such that rigid fixation of plate 31 to the first vertebra V1is achieved. Slots 35 are positioned over second vertebra V2, andinclude a second end 43 and a first end 44. As shown in FIG. 1, screw 50is initially is inserted at second end 43 of slot 35, allowingsubsequent translation of screw 50 in slot 35 from second end 43 tofirst end 44. For the purposes of clarity, only a single screw 50 isshown in slot 35; however, it is contemplated that bone screws areinserted in both slots 35. Bone screws 50 inserted in intermediate slots32 also translate from the second end 48 to first end 49 (FIG. 15) ofslot 32.

[0053] Once screws 50 are placed through holes 34 and in slots 32 and35, washer 90 of retainer assembly 33 may be translated to its lockedcondition shown in FIG. 2. In the locked condition, body portions 93,94, 95 of washer 90 retain the heads of the inserted screws 50 in holes34 and slots 32, 35 and prevent the screws from backing out of plate 31.In order to translate the retainer assembly 33 to its locked condition,locking screw 85 is threaded into a corresponding fastener bore 70 inplate 31. This downward threading of locking screw 85 causes the taperedcountersink 92 of washer 90 to ride along the head of locking screw 85until locking screw 85 contacts the first end of aperture 91. Thistranslates washer 90 along axis L to its locked condition, where thewasher 90 retains bone screws 50 in plate 31.

[0054] Bone screws 50 are allowed to translate within slots 35 andintermediate slots 32 from the second end of the slots to the first endof the slots while retainer assembly 33 retains bone screws 50 in plate31 and prevents screw backout. As shown in FIG. 3, the screw positionedin slot 35 has translated from second end 43 to first end 44. Thetranslation of screw 50 is limited by contact of screw 50 with first end44. The amount of translation may also be controlled by providing bonescrews in intermediate slots 32. Thus, the amount of translation of thespinal column segment can be limited by the length of slots 32, 35.

[0055] Referring now to FIGS. 4(a)-4(f) and FIGS. 5(a)-5(f), severalembodiments of elongated plate 31 and washer 90 are depicted. It isunderstood that the anterior plating system 30 according to the presentinvention can be readily adapted for fixation to several vertebrae bymodifying the length of plate 31 and the number and arrangements ofholes 34, second slots 35, and intermediate slots 32. Paired slots 32,35 and paired holes 34 at each of the vertebrae provide, at a minimum,for at least two bone screws 50 to be engaged into each respectivevertebrae. The placement of two or more screws in each vertebral bodyimproves the stability of the construct. It is one object of the presentinvention not only to provide for multiple screw placements in eachvertebral body, but also to provide means for retaining the bone screwsin plate 31 to prevent back out or loosening of the screws. The presentinvention contemplates various specific embodiments for a plate 31 thatis provided in lengths that range from 19 millimeters (hereinafter “mm”)to 110 mm, and an overall width of about 17.8 mm. However, otherdimensions for the length and width of plate 31 are also contemplatedherein.

[0056] The plate 31 of FIGS. 1-3 is sized to span four vertebrae andincludes a first node 36, a second node 37, and two intermediate nodes38. In FIGS. 4(a) and 5(a), plate 31 a and washer 90 a are sized spantwo vertebrae. Plate 31 a has holes 34 a at first node 36 a and holes 34a at second node 37 a Plate 31 a is provided with washer 90 a thatresides in groove 39 a and is translatable to retain bone screws inholes 34 a. In this embodiment, plate 31 a provides rigid fixation ateach vertebra. A modification of plate 31 a is depicted FIGS. 4(b) and5(b). The holes at the second vertebral node are replaced with slots 35b at second node 37 b. A washer 90 b resides in groove 39 b and istranslatable to retain bone screws in holes 34 b and slots 35 b.

[0057] Plate 31 c and washer 90 c of FIGS. 4(c) and 5(c) similarlyprovide for instmentation at two vertebrae. Plate 30 c has a recessportion between nodes 36 c and 37 c. Washer 90 c resides in groove 39 cand is translatable to retain lock screws in holes 34 c and slots 35 c.It should be noted that the plates of FIGS. 4(a)-4(c) span twovertebrae, and preferably do not include notch 40 on the second end ofthat plate as do the plates sized to span three or more vertebrae.

[0058] Plate 31 d and washer 90 d of FIGS. 4(d) and 5(d) are providedfor instrumentation at three vertebrae. Plate 31 d has first vertebralnode 36 d, second vertebral node 37 d, and intermediate node 38 d.Washer 90 d resides in groove 39 d and is translatable to retain bonescrews in holes 34 d and slots 32 d, 35 d. Plate 31 e and washer 90 e ofFIGS. 4(e) and 5(e) are provided for instrumentation at five vertebrae.Plate 31 e has first vertebral node 36 e, second vertebral node 37 e,and three intermediate nodes 38 e. Washer 90 e resides in groove 39 eand is translatable to retain bone screws in holes 34 e and slots 32 e,35 e. Plate 31 f and washer 90 f of FIGS. 4(f) and 5(f) are provided forinstrumentation at six vertebrae, Plate 3 if has first vertebral node 36f, second vertebral node 37 f, and four intermediate nodes 38 f. Washer90 f resides in groove 39 f and is translatable to retain bone screws inholes 34 f and slots 32 f, 35 f.

[0059] Referring now to FIG. 6, the details of bone engaging fastener orscrew 50 are shown. Bone screw 50 is preferably configured forengagement in the cervical spine, and includes threaded shank 51 that isconfigured to engage a cancellous bone of the vertebral body. Thethreaded shank may be provided with self-tapping threads, although it isalso contemplated that the threads can require prior drilling andtapping of the vertebral body for insertion of screw 50. It is preferredthat the threads on shank 51 define a constant outer diameter d2 alongthe length of the shank. It is also preferred that shank 51 has a rootdiameter that is tapered along a portion of the length of the shank andincreases from the tip of shank 51 to a diameter d1 at an intermediateor cylindrical portion 52.

[0060] Intermediate portion 52 extends between shank 51 and a head 54 ofscrew 50. The threads on shank 51 extend into portion 52 by a thread runout 53. According to standard machining practices, cylindrical portion52 includes a short segment that does not bear any threads This segmentof cylindrical portion 52 interfaces or contacts with a plate thicknessat hole 34 or slot 32, 35 through which bone screw 50 extends. Thisshort segment has an outer diameter d1. The head 54 of screw 50 includesa tool recess 55 configured to receive a driving tool. In one specificembodiment, tool recess 55 is a hex recess, or in the alternative, anytype of drive recess as would occur to those skilled in the art. Head 54includes a truncated or flattened top surface 56 having a diameter d4. Aspherical surface 57 extends from cylindrical portion 52 to a shoulder59. Shoulder portion 59 has a diameter d5. An inclined surface 58extends between shoulder 59 and truncated top surface 56. Inclinedsurface 58 forms an angle A₁ with top surface 56.

[0061] It is contemplated that screw 50 may be provided with shank 51having a length that varies from about 10 mm to about 24 mm. In onespecific embodiment of screw 50, the threads have diameter d2 of about4.5 mm. In another specific embodiment, the diameter d2 is about 4.0 mm.In both specific embodiments, cylindrical portion 52 has a diameter d1of about 4.05 mm. Cylindrical portion 52 has an unthreaded segment witha height h1 that is determined by standard machining practices forthread run-out between a shank and screw head. Height h1 and diameter d1of cylindrical portion 52 are sized to achieve a snug fit between screw50 and plate 31 in hole 34 or slot 32, 35 through which screw 50 isplaced. Head 54 is provided with height h2, outer diameter d5 atshoulder 59, diameter d4 at top surface 56, and inclined surface 54angle A₁ such that the head 54 is nested within its corresponding slot32, 35 or hole 34 and recessed below the top surface of the plate.Although reference has been made to specific dimensions in this specificembodiment, it should be understood that the present invention alsocontemplates other dimensions and configurations for screw 50. It shouldalso be understood that bone screws used to secure plate 31 can eachhave a different length and diameters associated therewith, and need notcorrespond exactly to the other bone engaging fasteners used in theconstruct.

[0062] The details of locking screw 85 are provided in FIG. 7. Lockingscrew 85 includes a shank 86 having machine threads thereon. In onespecific embodiment, locking screw 85 terminates in a sharp point 88that permits penetration into the vertebral body when locking screw 85is secured in threaded fastener bore 70. Head 87 includes a lowerconical surface 89 configured to mate with aperture 91 of washer 90.Head 87 further includes a tool recess 87 a for receiving a driving tooltherein.

[0063] Further details and embodiments of washer 90 of retainer assembly33 are provided in FIGS. 8(a)-8(k). Washer 90 includes second bodyportion 95, first body portion 93, and if necessary, one or moreintermediate body portions 94. A connecting portion 98 extends betweenand connects each of the body portions 93, 94, 95. Washer 90 has a topsurface 100 a and a bottom surface 100 b. Each body portion 94, 95defines an aperture 91 extending between top surface 100 a and bottomsurface 100 b. Aperture 91 has a tapered countersink portion 92therearound adjacent top surface 100 b. Aperture 91 allows passage ofshank 86 of locking screw 85 therethrough, and countersink 92 ispreferably configured to mate with conical surface 89 and seat lockingscrew 85 at various positions along the length of aperture 91.Preferably, countersink portion 92 is sloped toward bottom surface 100 bfrom second end 97 to first end 96. The mating conical features betweenlocking screw 85 and aperture 91 provide a self-translating capabilityfor washer 90 relative to plate 31 as locking screw 85 is tightened intofastener bore 70 of plate 31.

[0064] Body portions 93, 94, 95 have a width W1 that is greater than awidth W2 of connecting portion 98. The width W1 and length of bodyportions 93, 94, 95 are configured so that the body portions overlapwith recess 45 of holes 34 and recesses 46, 47 of slots 32, 35. The bodyportions 93, 94, 95 retain the heads of bone screws extending throughthe holes and slots of plate 31 when washer 90 resides in groove 39 andis in the locked condition of FIG. 2. The width W2 and the length of theconnecting portions 98 are configured to allow insertion of screws inholes 34 and slots 32, 35 when washer 90 is in the unlocked condition ofFIG. 1.

[0065] In FIGS. 8(a) and 8(b) there is shown second body portion 95 ofwasher 90. Aperture 91 has countersink portion 92 that is tapered alongthe length of aperture 91. Aperture 91 has a width W3 at bottom surface100 b of washer 90. Countersink portion 92 has a width that varies alongthe length of aperture 91 and is greater than width W3. Countersinkportion 92 has a radius R1 at second end 97 and a radius R2 at first end96 at top surface 100 a. It is preferred that R1 is less than R2 and thewidth of countersink portion 92 increases from second end 97 towardsfirst end 96. Aperture 91 has a chord length S1 extending between thecenter of radius R1 and the center of radius R2. Body portion 95 furtherincludes a transition portion 99 that extends between connecting portion98 and body portion 95.

[0066] Intermediate body portion 94 of FIGS. 8(c) and 8(d) is similar inmany respects to second body portion 95 of FIGS. 8(a) and 8(b), and alsoincludes an aperture 91 having a tapered countersink portion 92.However, intermediate body portion 94 has a connecting portion 98extending in both directions therefrom. A second transition portion 98 aextends between second connecting portion 98 and body portion 94. Bodyportion 94 has a chord length S1 between the center of radius R1 and thecenter of radius R2.

[0067] Tapered countersink 92 of aperture 91 provides a self-translatingcapability of the washer 90. This is because the washer 90 is translatedrelative to plate 31 as the locking screw 85 is threaded into threadedbore 70. The camming conical surface 89 of screw 85 advances downwardalong the tapered portion of the wall of countersink portion 92 ofaperture 91.

[0068] FIGS. 8(e) and 8(f) show first body portion 93. First bodyportion 93 is also similar to second body portion 95. However, in oneembodiment, first body portion 93 includes an aperture 91′ having acountersink portion 92′ that is not tapered along its length to providea self-translating capability for washer 90 like the countersinkportions 92 of body portions 94 and 95. Rather, after washer 90 istranslated relative to plate 31 as described above, locking screw 85will already be positioned at first end 96′, and may thereafter bethreaded into bore 70 and seated within countersink portion 92′.Alternatively, the surgeon may slide the washer by hand or with a toolto its translated position, and lock the washer in its translatedposition by seating locking screw 85 into countersink 92′ at first end96′. Countersink 92′ has a definite location at second end 96′ forseating locking screw 85, providing a reference for the surgeon toconfirm that washer 90 has been translated to its locked position. Itshould be understood, however, that it is also contemplated herein thatbody portion 93 could also be provided with aperture 91 like bodyportions 94 and 95 as shown in FIGS. 1-3.

[0069] Referring now to FIG. 8(g), a cross-sectional view of washer 90is provided through aperture 91 of body portion 94, 95. Washer 90 has anouter surface 104 configured to overlap bone screws 50 in slots 32, 35without contacting inclined surface 58 of screws 50 when retainerassembly 33 is in its locked condition. Outer surface 104 extends frombottom surface 100 b to a shoulder 103. Shoulder 103 extends betweeninclined surface 104 and top surface 100 a. Inclined surface 104 formsan angle A₂ with respect to bottom surface 100 b. Washer 90 defines athickness t1 between top surface 100 a and bottom surface 100 b, and ashoulder height of t2 from bottom surface 100 b. Washer 90 has a widthW7 along bottom surface 100 b at aperture 91.

[0070] Referring now to FIG. 8(h), a cross-sectional view of washer 90is provided through aperture 91 or 91′ of body portion 93. Washer 90 hascontact surface 106 configured to contact inclined surface 58 of screws50 when retainer assembly 33 is in its locked condition. Contact surface106 extends from bottom surface 100 b to a shoulder 105. Shoulder 105extends between contact surface 106 and top surface 100 a. Contactsurface 106 forms an angle A₃ with respect to bottom surface 100 b thatis configured to mate with and provide surface contact with inclinedsurface 58 of bone screw 50. Washer 90 defines a thickness t3 betweentop surface 100 a and bottom surface 100 b, and a shoulder height of t4from bottom surface 100 b.

[0071] In one specific embodiment of the washer 90, the body portionshave a width W1 and connecting portion have width W2 that is based onthe spacing between the centerlines of the paired slots and holes of theplates and the overall width of the plate. The width W3 of aperture 91in the specific embodiment is sized to accommodate the shank 86 oflocking screw 85 without head 87 passing therethrough. The length ofbody portions 94 and 95 varies based on the length and spacing betweenslots 32, 35 and holes 34 in plate 31. Preferably, the body portions 94,95 have a length sufficient to overlap substantially the entire lengthof slot 32, 35 when retainer assembly 33 is in its locked position. Thetapered countersink portion 92 of aperture 91 has radius R1 thattransitions to radius R2 along the chord length S1. Thickness t1 is lessthan thickness t3, and shoulder height t4 is less than shoulder heightt2. Body portion 93 has a width W8 along bottom surface 100 b that isgreater than width W7 of body portions 94, 95. Angle A₂ is preferablyless that angle A1. The dimensions of washer 90 are preferably arrangedso that body portions 94, 95 do not contact the screw heads nested inslots 32, 35 to facilitate translation of the screws in slots 32, 35.Body portion 93 contacts the screw heads nested in holes 34 to furtherenhance the fixed orientation between screws 50 and plate 31 in holes34. Although reference has been made to the dimensional attributes ofthis specific embodiment, it should be understood that the presentinvention also contemplates other orientations and dimensionalrelationships for washer 90.

[0072] The present invention also contemplates a retainer assembly inwhich individual washers are provided at each node for retaining screwsin holes 34 and slots 32, 35 of plate 31. Referring now to FIGS. 8(i)and 8(j), a slot washer 195 and a hole washer 193 are provided. Slotwasher 195 is similar to body portion 95 of washer 90 and hole washer193 is similar to body portion 93 of washer 90, both of which aredescribed above. Elements that are alike bear the same reference numberas the corresponding element of body portions 95, 93. Slot washer 195and hole washer 193 do not have a connecting portion 98 extending toanother washer. Slot washer 195 has a body portion 198 with a length S2that varies and is sized to correspond to the length of the adjacentslot 32, 35 when washers 195 are positioned on plate 31. Slot washer 195does not have a connecting portion 98 extending to another washer. Holewasher 193 has a body portion 199 with a length S3 that varies and issized to correspond to the length of the plate adjacent hole 34 whenwasher is positioned on plate 31.

[0073] In FIG. 8(k) an alternate embodiment of washers 193 and 195 isprovided and designated at 193′, 195′ respectively. Washers 193′, 195′are the same as washers 193, 195 described above, except for aperture191. Aperture 191 does not have a tapered countersink, but rather has asemi-circular countersink portion 192 only at first end 196. Countersinkportion 192 provides a single position for locking screw 85 to lock thewasher 193′, 195′ to plate 31 after the washer 193′, 195′ has beentranslated relative to plate 31 by the surgeon. Washers 193′, 195′ havebody portion 198′, 199′ with length S4 that varies as described abovewith respect to length S2 and S3.

[0074] Referring now to FIGS. 9-18, further details of plate 31 will bediscussed with reference to illustrations of first node 36, second node37, and intermediate node 38. In FIGS. 9-11, first node 36 of plate 31is depicted. It is preferred that holes 34 are identical and symmetricalabout axis L. Hole 34 includes recess 45 adjacent top surface 41. Holes34 include a cylindrical bore 77 having generally vertical sidewallsadjacent bottom surface 42. Cylindrical bore 77 extends between recess45 and bottom surface 42 of plate 31, and has a diameter D1. Cylindricalbore 77 has axis 72 b that is offset at angle A₅ from an axis 72 a thatextends normal to plate 31 as shown in FIG. 10. Recess 45 has a partialspherical portion 45 a defined about a central axis 72 b. Axis 72 b isoffset from axis 72 a by angle A₅. Offset angle A₅ directs bone screwsinserted into holes 34 toward the first end of plate 31. Furthermore, asshown in FIG. 11, axes 72 a converge below the bottom surface 42 ofplate 31 at angle A₄ with respect to an axis 72 c that extends along thecenterline of plate 31 perpendicular to axis L. Recess 45 intersectsgroove 39 at intersecting portion 45 c. Spherical portion 45 a isconfigured to mate with spherical surface 57 of bone screw 50, allowingat least a portion of head 54 to be recessed below top surface 41 ofplate 31.

[0075] To facilitate insertion of drill guides, drills and the bonescrews 50, recess 45 also includes a flared portion 45 b that extends ina superior direction from axis 72 b. In one embodiment, recess 45includes a wall that parallels bore 77 and extends between betweenspherical portion 45 a and flared portion 45 b to further facilitateinsertion and maintenance of a drill guide in recess 45.

[0076] In one specific embodiment, spherical portion 45 a has a diameterthat mates with the diameter of spherical surface 57 of screw 50, and isslightly larger than diameter d5 of head 54 of bone screw 50. Thecylindrical bore 77 of hole 34 has a diameter D1 of 4.1 mm, which isslightly larger than the diameter d1 of intermediate portion 52 of screw50. This portion of the screw contacts bore 77 and assumes a fixedorientation with respect to plate 31. In this specific embodiment,offset angle A₅ is about 12.6 degrees and convergence angle A₄ is about6 degrees relative to axis 72 c. Although reference has been made to thedimensional attributes of this specific embodiment, it should beunderstood that the present invention also contemplates otherdimensions.

[0077] Referring now to FIGS. 12-14, second vertebral node 37 isdepicted. Vertebral node 37 includes slots 35 that are preferablyidentical and symmetrical about axis L. Slot 35 includes slotted bore 78adjacent bottom surface 42 of plate 31 having generally verticalsidewalls extending between second end 43 and first end 44. Slotted bore78 extends between bottom surface 42 and recess 47 adjacent top surface42. Bore 78 has a width W5 and a chord length S4, and has a central axis75 b extending through plate 31. Recess 47 has a spherical portion 47 aabout central axis 75 b that extends around slot 35. As shown in FIG.13, central axis 75 b is offset from axis 75 a that extends normal toplate 31 by angle A₅. Offset angle A₅directs bone screws inserted intoslot 35 towards the second end of plate 31. It should be noted that slot35 allows insertion of a bone screw at angles less than A₅ in slot 35,and bone screw 50 may be positioned within slot 35 at any locationbetween ends 43 and 44. However, retaining assembly 33 provides forinsertion of bone screws 50 at second 43 as would be clinicallydesirable for settling. Furthermore, as shown in FIG. 14, axes 75 bconverge below the bottom surface 42 of plate 31 at angle A₅ withrespect to axis 72 c.

[0078] Spherical portion 47 a is configured to mate with sphericalsurface 57 of bone screw 50, allowing at least a portion of head 54 tobe recessed below top surface 41 of plate 31. To facilitate insertion ofdrill guides, drills and the bone screws 50, recess 47 also includes aflared portion 47 b that extends around spherical portion 47 a. In oneembodiment, it is contemplated that recess 47 include a wall thatparallels bore 78 extending between spherical portion 47 a and flaredportion 47 b to further facilitate maintenance and insertion of a drillguide in recess 47. Recess 47 intersects groove 39 at overlap portion 47c, as shown in FIG. 14. The second end of second node 37 includes notch40 having radius R4 centered about axis L. It is also contemplatedherein that plate 31 is provided without notch 40, as shown in FIGS.4(a)-4(c).

[0079] In a preferred embodiment, slot 35 includes ramp 60 extendingbetween bore 78 and flared portion 47 b at second end 43. Ramp 60 is notconfigured to allow spherical surface 57 of screw 50 to seat therein,but has an orientation that causes second end 43 of slot 35 and screw 50to separate as screw 50 is threaded into slot 35. Spherical surface 57of head 54 provides camming action along the ramp 60 until head 54 seatsin recess 47 at a position spaced a distance from second end 43. Thiscamming action applies a dynamic compression load to the spinal columnportion. The amount of compression applied to the spinal column portionis controlled by the length of ramp 60 from second 43 to the position inslot 35 where screw 50 seats in recess 47. It should be understood thatslot 35 may also be provided without ramp 60.

[0080] In one specific embodiment, spherical portion 47 a has a diametersized to mate with spherical surface 57 of screw 50, and is slightlylarger than diameter d5 of head 54 of bone screw 50. Slotted bore 78 hasa width W5 of about 4.1 mm, which is slightly larger than the diameterd1 of intermediate portion 52 of screw 50. The cylindrical portion 52 ofbone screw 50 contacts plate 31 in bore 78 and prevents rotation ofscrew 50 transverse to axis 72 c. The chord length S4 varies dependingupon the length of the slot 35 needed for the particular application ofplate 31 and patient anatomy. In this specific embodiment, offset angleA₅ is about 12.6 degrees and convergence angle A₄ is about 6 degreesrelative to an axis 72 c. Although reference has been made to thedimensional attributes of this specific embodiment, it should beunderstood that the present invention also contemplates otherdimensions.

[0081] Referring now to FIGS. 15-17, various views of intermediate node38 are depicted. Vertebral node 38 includes slots 32 that are preferablyidentical and symmetrical about axis L. Slot 32 includes slotted bore 79adjacent bottom surface 42 of plate 31 having generally verticalsidewalls extending between a second end 48 and a first end 49. Slottedbore 79 extends between bottom surface 42 and recess 46 adjacent topsurface 42. Bore 79 has a width W5 and a chord length S5, and has acentral axis 76 a extending through plate 31. Recess 46 has a sphericalportion 46 a that extends around slot 35. As shown in FIG. 16, centralaxis 76 a generally extends normal to plate 31. However, as shown inFIG. 17, the axes 76 a converge below the bottom surface 42 of plate 31at angle A₄ with respect to axis 72 c. It should be noted that slot 32allows insertion of bone screws 50 at various angles with respect toaxis 76 a.

[0082] Spherical portion 46 a is configured to mate with sphericalsurface 57 of bone screw 50, allowing at least a portion of head 54 tobe recessed below top surface 41 of plate 31. To facilitate insertion ofdrill guides, drills and bone screws 50, recess 46 also includes aflared portion 46 b that extends around spherical portion 46 a. In oneembodiment, a wall paralleling bore 79 extends between spherical portion46 a and flared portion 46 b to further facilitate insertion andmaintenance of a drill guide in recess 46. Screw 50 may be placed withinintermediate slot 32 between ends 48 and 49. However, it is preferredthat the screw is inserted initially at second end 48, thus allowingcompression loading of the spinal column segment. Recess 46 intersectsgroove 39 at overlap portion 46 c, as shown in FIG. 17.

[0083] In one specific embodiment, spherical portion 46 a has a diametersized to mate with spherical surface 57 of screw 50, and is slightlylarger than diameter d5 of head 54 of bone screw 50. The slotted bore 79has a width W5 of about 4.1 mm, which is slightly larger than thediameter d1 of intermediate portion 52 of screw 50. Cylindrical portion52 of bone screw 50 interfaces with plate 31 in bore 79 such thatangular adjustment of screw 50 transverse to axis 72 c is prevented. Thechord length S5 varies depending upon the length of slot 35 needed forthe particular application of plate 31 and patient anatomy. In thisspecific embodiment convergence angle A₄ is about 6 degrees relative toan axis 72 c. Although reference has been made to the dimensionalattributes of this specific embodiment it should be understood that thepresent invention also contemplates other dimensions.

[0084] Referring now to FIG. 18, a cross-sectional view of plate 31 isprovided through line 18-18 of FIG. 15. Groove 39 has a width W6 at topsurface 41 of plate 31. Groove 39 has bottom surface 73 extendingbetween inclined sidewalls 74. Sidewalls 74 extend between bottomsurface 73 of groove 39 and top surface 41 of plate 31. It iscontemplated that the groove 39 has a depth sufficient to accommodatethe washer 90 so as to minimize protrusion of washer 90 above topsurface 41 of plate 31.

[0085] To accommodate the anterior application of the fixation plateassembly 30, the plate is curved in two degrees of freedom.Specifically, the bottom surface 42 of the plate can be curved along alarge radius R, centered in a vertebral plane containing central axis L,as shown schematically in FIG. 16, to accommodate the lordotic curvatureof the cervical spine. In addition, bottom surface 42 forms amedial/lateral curvature C, as shown in FIG. 18, to correspond to thecurvature of the vertebral body. It is understood that plate 31 can alsobe bent as needed to accommodate the particular spinal anatomy andvertebral pathology.

[0086] Referring now to FIG. 19a, a partial sectional view of fixationplate assembly 30 at holes 34 is provided with screws 50 engaged tovertebra V1 and retainer assembly 33 in the locked position. A pair ofscrews 50 are disposed within the respective holes 34 so that thethreaded shanks 51 project beyond the lower surface 42 of plate 31 intothe vertebral body V1. The intermediate portion 52 of screw 50 extendsthrough the bore 77 of the hole 34. Spherical surface 57 of head 54contacts recess 45 of hole 34 when screw 50 is seated therein. Theintermediate portion 52 provides a snug fit for screw 50 in the bore 77so that screw 50 is not able to pivot with respect to plate 31.

[0087] Referring to FIG. 19b, a partial sectional view of fixation plateassembly 30 at slots 32 or 35 is provided with screws 50 engaged tovertebra V1 and retainer assembly 33 in the locked position. A pair ofscrews 50 are disposed within respective slots 32, 35 so that threadedshanks 51 project beyond lower surface 42 of plate 31 into thecorresponding vertebral body V2, V3, or V4. Cylindrical portion 52 ofscrew 50 extends through bores 78, 79 of slots 35 and 32, respectively.Spherical surface 57 of head 54 contacts recesses 46, 47 of slots 32, 35when screw 50 is seated therein. Cylindrical portion 52 provides a snugfit for screw 50 in bores 78, 79 so that screw 50 is not able to pivotor translate with respect to axis 72 c of plate 31. Of course, screws 50inserted into slots 32 or 35 are able to translate along the length ofslots 32, 35 as described above. It should be understood that thepresent invention also contemplates various embodiments of plate 31 thatuse variable angle screws capable of assuming universal angularorientation with respect to plate 31 in slots 32, 35 and holes 34.

[0088] In order to ensure screws 50 are retained within plate 31,retainer assembly 33 is moved to its locked position where it contactsthe heads 54 of bone screws 50 in holes 34. Locking screw 85 is threadedinto threaded fastener bore 70 of plate 31 to translate washer 90 fromits unlocked position to its locked position, as described above, and todraw contact surface 106 into contact with inclined surface 58 of screw50 as shown in FIG. 19aContact surface 106 preferably applies a downwardforce onto head 54 to firmly seat the screw heads within the platerecesses and further fix screw 50 in hole 34. In a preferred embodiment,this downward force is exacted by washer 90 as surface 106 contactsinclined surface 58. As shown in FIG. 19b, outer surface 104 of washer90 does not contact the heads of bone screws 50 in slots 32, 25. Outersurface 104 overlaps the bone screws 50 to retain bone screws in slots32, 35. Outer surface 104 will contact the heads of the bone screws ifthe bone screws backout from slots 32, 35. It is preferred that bottomsurface 100 b of washer 90 does not contact bottom surface 73 of groove39.

[0089] In a further aspect of the invention, the retainer assembly 33may be loosely fixed on plate 31 so the surgeon need not fiddle withapplying retainer assembly 33 to plate 31 during surgical procedures.The locking fasteners 85 are pre-inserted through apertures 91 of washer90 and partially threaded into fastener bores 70. Washer 90 is initiallypositioned such that the second end of each aperture 91 is positionedadjacent locking screw 85. After positioning screws 50 through the holesand slots of plate 31, locking fasteners 85 are advanced further intobores 70 and along tapered portions 92 of apertures 91 to translatewasher 90 to a locked condition and retain bone screws 50 in plate 31.

[0090] As previously mentioned, sharp point 88 of locking screw 85 ispreferably configured to penetrate the cortical bone. In one embodiment,sharp point 88 will penetrate the vertebra when plate 31 is initiallypositioned on the bone. In this instance, locking screw 85 helps locateand temporarily stabilize the plate on the vertebra as the bone screws50 are engaged to the vertebra. This temporary location feature providedby locking screw 85 can also be used to maintain the position of plate31 on the vertebra as a drill guide is used to drill and tap thevertebrae to receive bone screws 50.

[0091] According to another aspect of the invention, there are providedinstruments and techniques for securing plate 31 to vertebrae of aspinal column segment and for applying a compression load to a graft orimplant placed in the spinal column segment. Referring to FIGS.20(a)-20(f), a guide 150 includes a handle 152, a template 154, and arm153 extending therebetween. Preferably, arm 153 extends outward from thespine and is bent so that handle 152 parallels the spine, positioninghandle 152 out of the way of the surgeon. Template 154 includes a secondend 155 that defines a notch 158. Template 154 also includes first end156 having a projection 156 a extending downward therefrom towardsvertebral body V2. Template 154 further defines a pair of slots 157between second end 159 and first end 156.

[0092] The surgeon selects a guide 150 with a template 154 sized toposition notch 158 at the desired location on vertebra V2 and placesguide instrument 150 on vertebral body V2. Notch 158 is located onvertebra V2 by placing projection 156 a in abutting contact with theendplate of vertebra V2 in disc space D. Slots 157 provide a visualindication to the surgeon of the range of positions available for screwinsertion into the vertebral body through slots 35 of plate 31. Ifdesired, the surgeon can obtain a desired position or location of notch158 and the desired available range of bone screw positions on vertebraV2 by selecting a guide having a different sized template 154.

[0093] Referring now to FIG. 20(b), after the notch is in the desiredposition on vertebra V2, a compression pin 170 is placed into vertebraV2 guided by notch 158. Pin 170 includes a lower end 171 having athreaded portion (not shown) for attaching pin 170 to vertebra V2. Theattachment portion is preferably threaded to screw into vertebra V2, butmay also be smooth with a spiked tip for insertion into the vertebra.Pin 170 also includes tool engagement portion 172 to facilitateinstallation of pin 170 to the vertebral body. It is also contemplatedthat the surgeon can place pin 170 on the vertebral body spaced awayfrom notch 158 if desired and the vertebral anatomy so allows.

[0094] After pin 170 is engaged to vertebra V2, guide 150 is removed anda sleeve 180 is placed over pin 170 as shown in FIG. 20(c). Sleeve 180has a hollow body 181 extending between a first end 186 adjacentvertebra V1 and a second end 184. A second end 174 of pin 170 preferablyextends from second end 184 of sleeve 180, allowing access to pin 170.Sleeve 180 includes enlarged portion 184 to facilitate placement andremoval of sleeve 180. It is contemplated that sleeve 180 has hollowinterior and an internal configuration that provides secure attachmentto pin 170. Body 181 includes cylindrical outer surface 182 with anouter diameter d6.

[0095] With sleeve 180 in its proper position, plate 31 is positionedwith notch 40 in abutting contact with outer surface 182 of sleeve 180,as shown in FIG. 20(d). The diameter d6 of sleeve 180 slightly less thanthe twice the radius of notch 40 so that notch 40 is nested aroundsleeve 180. Plate 31 is then secured to vertebra V1 by inserting screws50 through holes 34.

[0096] With plate 31 secured to the vertebra V1, sleeve 180 is removedfrom pin 170, as shown in FIG. 20(e), forming a gap 177 between pin 170and notch 40. In a preferred embodiment, it is contemplated that gap 177is about 2 mm. However, other sizes for gap 177 are contemplated hereinbased on the desired compression to be applied.

[0097] Referring now to FIG. 20(f), a compression tool 290 is secured topin 170 and to slots 32 of plate 31. It is also contemplated that thecompression tool can be secured to plate 31 other than at slots 32 by,for example, engaging the sides of plate 31. Compression tool 290 has afirst arm 291 with a first foot 294 connected to pin 170. Second arm 292is connected to the second end of slots 32 via extensions 297 extendingfrom second foot 296. First arm 291 and second arm 292 are manipulatedby the surgeon to apply a compression load to the spinal column segment.The amount of applied load is limited by gap 177 between pin 170 andnotch 40. For example, in the specific embodiment where gap 177 is 2 mm,the spinal column portion is compressed 2 mm.

[0098] Bone screws 50 are inserted into slots 35 with compression tool290 maintaining the compression load. With ramp 60 at second 43 of slot35, an additional amount of dynamic compression is achieved with screwinsertion in slots 35, as described above. With screws 50 seated at end43 of slots 35, compression tool 290 may be removed without release ofthe compression load. Additional bone screws may be inserted intointermediate slots 32. Washer 90 may then be translated as describedabove to retain bone screws 50 in plate 31. It should be note that it iscontemplated herein that compression tool 290 and pin 170 are preferablyonly used with plates providing instrumentation at three or morevertebra. However, utilization of a compression tool configured toengage a plate for providing instrumentation at two vertebrae is notprecluded.

[0099] Referring now to FIGS. 21(a)-21(c), further details ofcompression tool 290 are provided. Tool 290 has first arm 291 havingfirst foot 294 extending therefrom. First foot 294 defines recess 293for receiving the pin 170. Second arm 292 has second foot 296 extendingtherefrom. Second foot 296 includes extensions 297 extending downwardtherefrom configured to engage intermediate slots 32 of plate 31.Extensions 297 preferably include recesses 307 that are configuredcontact the second ends of intermediate slots 32. It is alsocontemplated that extensions 297 have a curved bottom surface 308 thatcorresponds to the medial lateral curvature of the vertebral bodies.

[0100] First arm 291 has a reduced thickness portion 299 extendingthrough a passage 295 formed in second arm 292, and is pivotally coupledto second arm 292 with pin 299. First arm 291 has curved handle portion306 having a projection 303 extending therefrom. Second arm 292 has ahandle 305. A ratchet bar 301 is pivotally coupled to second arm 292 viacoupling 302. Preferably, ratchet bar 301 is spring-biased towardsprojection 303. Serrations 304 formed on the bottom side of ratchetmechanism 301 provide for selective engagement with projection 303 onfirst arm 291.

[0101] The first and second arms are compressed towards one another toapply the compressive load to the vertebral segment. Projection 303engages the serrated bottom of ratchet bar 301 to prevent relaxation ofthe arms and allows the surgeon to maintain the compression load duringinsertion of bone screws 50 within slots 35. Ratchet bar 301 may belifted against its spring bias away from arm 291 to disengage ratchetbar 301 from projection 303. Arms 291, 292 may then be moved away fromone another to release compression tool 290 from pin 170 and plate 31.

[0102] While compression tool 290 has been illustrated and described indetail, the present invention also contemplates other tools capable ofbeing secured between pin 170 and plate 31 to provide a compression loadto the spinal column segment. For example, referring now to FIGS. 22(a)and 22(b), it is contemplated that a compression tool may include one ormore angular modifications to first arm 391 and second arm 392 tofacilitate access to plate 31 and pin 170 at the surgical site. Firstarm 391 has a lower portion 391 a forming angle B1 with first foot 396.First foot 396 has extensions 397 extending therefrom that are similarto extensions 297 of tool 290. First arm has an upper portion 391 c thatterminates with curved handle 406. Curved handle 406 has projection 403extending therefrom to engage a ratchet bar extending from second arm392. Arm 391 has a vertical extension 391 b extending between lowerportion 391 a and upper portion 391 c. Angle B2 is formed between lowerportion 391 a and vertical portion 391 b. Angle B1 is formed betweenvertical portion 391 b and upper portion 391 c. Vertical portion 391 bas a region of reduced thickness 399 for connection with second arm 392.

[0103] Second arm 392 has a lower portion 392 a forming angle B1 withsecond foot 394. Second foot 394 has a recess (not shown) for receivingpin 170 and is similar to recess 293 of tool 290 described above. Secondarm 392 has an upper portion 392 c that terminates with handle 405.Upper portion 392 c has ratchet bar 401 with serrations 404. Ratchet bar401 is pivotally coupled to arm 392 and spring-biased towards projection403. Ratchet bar 401 is similar to ratchet bar 301, but is preferablycurved along its length to accommodate the angular offsets in arms 391,392 while maintaining engagement between ratchet bar 401 and projection403. Arm 392 has a vertical extension 392 b extending between lowerportion 392 a and upper portion 392 c. Angle B2 is formed between lowerportion 392 a and vertical portion 392 b. Angle B1 is formed betweenvertical portion 392 b and upper portion 392 c. Vertical portion 392 bas a slot 395 of receiving reduced thickness portion 399 of verticalportion 391 b, where first and second arms are pivotally coupled via apin (not shown.)

[0104] In one specific embodiment of compression tool 290 and 390, angleB1 is about 120 degrees and angle B2 is about 150 degrees. However,other angular offsets in first and second arms of compression tools 190,290 are also contemplated herein as would occur to those skilled in theart.

[0105] While the invention has been illustrated and described in detailin the drawings and foregoing description, the same is to be consideredas illustrative and not restrictive in character, it being understoodthat only the preferred embodiment has been shown and described and thatall changes and modifications the come within the spirit of theinvention are desired to be protected.

What is claimed is:
 1. A bone fixation system for a portion of thespinal column, comprising: a plate having a length along a central axisextending longitudinally between a first end and a second end, and a topsurface and a bottom surface along said length, and said plate having aplurality of first openings and a plurality of second openings betweensaid surfaces, wherein: at least one of said plurality of first openingsis positioned adjacent said first end, said one first opening defining acircular hole having a first diameter adjacent said bottom surface; atleast one of said plurality of second openings is positioned adjacentsaid second end, said one second opening defining a slot having a firstwidth and a first length adjacent said bottom surface; bone engagingfasteners extending through said first and second openings, each boneengaging fastener having an elongated shank defining bone engagingthreads thereon and an enlarged head, said shank having a substantiallycylindrical portion with a third diameter less than said first diameterso said bone engaging fastener can be inserted through said one firstopening and said cylindrical portion contacts said plate in said onefirst opening so that said bone engaging fastener assumes a fixedorientation relative to said plate, said cylindrical portion thirddiameter also less than said second width so said bone engaging fastenercan be inserted through said one second opening from said top surface ofsaid plate and said head of said bone engaging fastener is translatablealong the length of said at least one second opening to maintaincompression of the spinal column portion.
 2. The bone fixation system ofclaim 1, wherein said second openings include a ramp that guides saidbone engaging fastener as it is inserted into said one second opening toprovide a dynamic compression load to the spinal column portion.
 3. Thebone fixation system of claim 1, whereby each of said at least one firstand second openings define a recess adjacent said top surface and saidenlarged head defines a partially spherical surface complementary tosaid recess of said at least one first and second openings.
 4. The bonefixation system of claim 3, wherein said head of said fastener includesa truncated top surface.
 5. The bone fixation system of claim 3, furthercomprising a retainer assembly for retaining said heads of said numberof bone engaging fasteners within said at least one first opening andsaid at least one second opening.
 6. The bone fixation system of claim5, wherein said retainer assembly includes: a first fastener boredefined in said plate adjacent said at least one first opening and asecond fastener bore defined in said plate adjacent said at least onesecond opening; a washer having at least a first aperture adjacent saidat least one first opening and a second aperture adjacent said at leastone second opening and a countersink portion communicating with each ofsaid apertures, said washer further having a body with portionsoverlapping said at least one first and second opening when said washeris in a first position relative to said at least one first and secondopenings, said body portions being arranged so that bone engagingfasteners can be inserted through said at least one first opening andsaid at least one second opening when said washer is in a secondposition relative to said at least one first and second openings; and alocking fastener for each of said apertures having a head configured tobe at least partially recessed within said countersink portion of saidwasher and having an elongated shank extending through said aperture andconfigured to engage said fastener bore of said plate.
 7. The bonefixation system of claim 6, wherein said plate further defines a groovein said top surface extending longitudinally along said plate, saidgroove being overlapping said at least one first and second openings,said first and second fastener bores being positioned within saidgroove.
 8. The bone fixation system of claim 5, wherein said retainerassembly includes a washer having a contact surface for contacting saidhead of said bone engaging fastener in said one first opening and anouter surface for overlapping said heads of said bone engaging fastenersin said one second opening.
 9. The bone fixation system of claim 1,further comprising a retainer assembly including: a first fastener boredefined in said plate adjacent said at least one first opening and asecond fastener bore defined in said plate adjacent said at least onesecond opening; a washer having at least a first aperture adjacent saidat least one first opening and a second aperture adjacent said at leastone second opening and a countersink communicating with each of saidapertures, said washer further having a surface configured to contactsaid head of said bone engaging fastener extending through said at leastone first opening; and a locking fastener for each of said apertureshaving a head configured to be at least partially recessed within saidcountersink portion of said washer and an elongated shank extendingthrough said aperture configured to engage said fastener bore of saidplate.
 10. The bone fixation system of claim 9, wherein said washer hasan outer surface that overlaps said head of said bone engaging fastenerextending through said at least one second hole without contacting saidhead.
 11. The bone fixation system of claim 9, wherein said platefurther defines a groove in said top surface extending longitudinallyalong said plate, said groove overlapping said at least one first andsecond openings, said first and second fastener bores being positionedwithin said groove.
 12. The bone fixation system of claim 1, whereinsaid elongated plated defines a plurality of vertebral nodes atlongitudinally spaced location along the plate.
 13. The bone fixationsystem of claim 12, wherein there are provided a pair of said firstopenings at one said vertebral nodes adjacent said first end of saidplate and a pair of said second openings at one of said vertebral nodesadjacent said second end of said plate.
 14. The bone fixation system ofclaim 13, wherein said openings of said pair of first openings aresymmetrically positioned about said central axis and said openings ofsaid pair of second openings are symmetrically positioned about saidcentral axis.
 15. A bone fixation system for a portion of the spinalcolumn, comprising: a plate having a length along a central axisextending longitudinally between a first end and a second end, a topsurface and a bottom surface along said length, said plate furtherdefining a plurality of first openings and a plurality of secondopenings between said surfaces, wherein: at least two of said firstopenings are circular, having a first diameter, and are positionedadjacent said first end; at least two of said second openings areslotted, having a first width and a first length, and are positionedadjacent said second end of said plate; bone engaging fastenersextending through said first and second openings, each bone engagingfastener having an elongated shank having bone engaging threads thereonand an enlarged head, said bone engaging fasteners configured forinsertion into said first and second openings from said top surface; andmeans retaining said heads of said bone engaging fasteners in said firstand second openings, said retaining means translatable from a firstposition allowing bone engaging fastener insertion into said first andsecond openings to a second position retaining said bone engagingfasteners in said first and second openings.
 16. The bone fixationsystem of claim 15, wherein said two first openings have a recessportion adjacent said top surface and said two second openings have arecess portion adjacent said top surface.
 17. The bone fixation systemof claim 16, wherein said heads of said bone engaging fasteners areconfigured to be at least partially recessed in said two first andsecond openings.
 18. The bone fixation system of claim 15, wherein saidtwo first and second openings each include a recess adjacent said topsurface and said enlarged head has a partially spherical surfacecomplementary to said recess of said two first and second openings. 19.The bone fixation system of claim 18, wherein said plate further definesa groove in said top surface extending longitudinally along said platefor receiving said retaining means therein, said groove overlapping saidrecesses.
 20. The bone fixation system of claim 15, wherein said head ofsaid bone engaging fastener has an inclined surface and said retainingmeans has a contact surface to contact said inclined surface of saidbone engaging fasteners extending through said two first openings. 21.The bone fixation system of claim 15, wherein retaining means includes:a first fastener bore defined in said plate adjacent said two firstopenings and a second fastener bore defined in said plate adjacent saidtwo second openings; a washer having a body defining at least a firstaperture adjacent said two first openings and a second aperture adjacentsaid two second openings and a countersink portion communicating witheach of said apertures, said washer further having a contact surfaceconfigured to contact said head of said bone engaging fastener extendingthrough said two first openings; and a locking fastener for each of saidapertures having a head configured to be at least partially recessedwithin said countersink portion of said washer and an elongated shankextending through said aperture and configured to engage said fastenerbore of said plate.
 22. The bone fixation system of claim 21, whereinsaid apertures of said washer each form a slot having a length extendinglongitudinally with the plate.
 23. The bone fixation system of claim 22,wherein at least one of said aperture countersink portion is taperedalong said length of said slot and has a width that increases along saidlength of said aperture from said second end towards said first end. 24.The bone fixation system of claim 22, wherein said at least one apertureis positioned adjacent said two second openings.
 25. The bone fixationsystem of claim 15, wherein said retaining means includes: a firstfastener bore defined in said plate adjacent said two first openings anda second fastener bore defined in said plate adjacent said two secondopenings; a washer having at least a first aperture adjacent said twofirst openings and a second aperture adjacent said two second openingsand a countersink portion communicating with each of said apertures,said washer further having a body with portions overlapping said twofirst openings and said two second openings when said washer is in afirst position relative to said two first and second openings, said bodyportions being arranged so that bone engaging fasteners can be extendedthrough said two first openings and said two second openings when saidwasher is in a second position relative to said two first and secondopenings; and a locking fastener for each of said apertures having ahead configured to be at least partially recessed within said taperedportion of said washer and an elongated shank extending through saidaperture and configured to engage said fastener bore of said plate. 26.The bone fixation system of claim 25, wherein said apertures of saidwasher form slots having a length extending in the direction of thelength of the plate.
 27. The bone fixation system of claim 26, wheresaid countersink communicating with each of said apertures has a widththat increases along the length of said aperture in a direction fromsaid second end towards said first end.
 28. A bone fixation system for aportion of the spinal column, comprising: four bone engaging fasteners,each having an enlarged head and a threaded shank; and an elongatedplate having a length extending between a first end and a second end andsized to span between at least two vertebrae, said plate defining a onepair of adjacent holes adjacent said first end and one pair of adjacentslots adjacent said second, each of said holes and said slots configuredto receive said threaded shank of a corresponding one of said boneengaging fasteners therethrough, wherein said bone engaging fastenersextending through said pair of holes fix said plate to said firstvertebra and said bone engaging fasteners extend through said slots tosecure said plate to said second vertebra, and said bone engagingfasteners received in said slots are enabled to translate in said slotsin a direction of the length of the plate to maintain compression on thespinal column portion.
 29. The bone fixation system of claim 28, whereinsaid plate has a top surface and a bottom surface and said holes andsaid slots each further include a recess adjacent said top surface. 30.The bone fixation system of claim 28, further including a retainerassembly having a washer configured to overlap each of said holes andslots and retain said bone engaging fasteners extending through saidholes and slots.
 31. The bone fixation system of claim 30, wherein saidhead of each of said bone engaging fasteners has an inclined surface andsaid washer has a contact surface configured to contact said inclinedsurface of said bone engaging fasteners extending through said pair ofholes.
 32. The bone fixation system of claim 30, wherein said plateincludes a first fastener bore defined in said plate between said pairof holes and a second fastener bore defined in said plate between saidpair of slots, and said retainer assembly further includes: said washerhas at least a first aperture adjacent said holes and a second apertureadjacent said slots and a countersink portion communicating with each ofsaid apertures; and a locking fastener for each of said apertures, saidlocking fastener having a head configured to be recessed within saidrecess of said washer and an elongated shank extending through saidaperture and configured to engage said fastener bore of said plate. 33.The bone fixation system of claim 32, wherein said elongated shank ofsaid locking fastener terminates in a sharp point for penetrating avertebral body.
 34. The bone fixation system of claim 33, wherein saidhead of said locking fastener defines a lower conical surface forcontacting said washer.
 35. A bone fixation system for a portion of aspinal column, comprising: six bone engaging fasteners, each having anenlarged head and a threaded shank; and an elongated plate having alength extending between a first end and a second end and sized to spanbetween at least three vertebrae, said plate defining one pair of holesover a first vertebra, one pair of intermediate slots over a secondvertebra, and one pair of slots over a third vertebra, each of saidholes and said slots configured to receive said threaded shank of acorresponding one of said bone engaging fasteners therethrough, whereinsaid bone engaging fasteners extending through said pair of holes fixsaid plate to said first vertebra and said bone engaging fastenersextend through said slots to secure said plate to said second vertebra,and said bone engaging fasteners received in said slots are enabled totranslate in said slots in a direction of the length of the plate tomaintain compression on the spinal column portion.
 36. The bone fixationsystem of claim 35, further including a retainer assembly having awasher configured to overlap each of said holes and slots and retainsaid bone engaging fastener extending through said holes and slots insaid plate.
 37. A fastener retainer assembly for an elongated platehaving a length extending between at least two vertebrae, the platedefining a number of openings therethrough for insertion of boneengaging fasteners to attach the plate to the at least two vertebrae,said retainer assembly comprising: a first fastener bore defined in saidplate adjacent at least one of the openings positioned over the firstvertebra and a second fastener bore defined in said plate adjacent atleast one the openings positioned over the second vertebra; a washerdefining at least a first aperture adjacent said at least one openingpositioned over the first vertebra and a second aperture adjacent saidat least one opening positioned over the second vertebra, said washerconfigured to retain said bone engaging fasteners extending through saidopenings in said plate; and a locking fastener for each of saidapertures, said locking fastener having an elongated shank extendingthrough said aperture and configured to engage said fastener bore ofsaid plate, said openings in said plate being positioned and configuredwherein said washer is movable between a first position enablinginsertion of said bone engaging fasteners into said at least oneopenings and a second position wherein said washer retains said insertedbone engaging fasteners in said plate.
 38. The retainer assembly ofclaim 37, wherein said apertures of said washer form slots having alength extending in the direction of the length of the plate.
 39. Theretainer assembly of claim 38, wherein each of said apertures include acountersink portion communication with said slot.
 40. The retainerassembly of claim 39, wherein said countersink portion of at least oneof said apertures is tapered and has a width that increases along thelength of said aperture from a second end to a first end.
 41. A fastenerretainer assembly for an elongated plate extending between at least twovertebrae, the plate defining a number of openings for insertion of boneengaging fasteners therethrough to secure the plate to the at least twovertebrae, and the plate defining at least one fastener bore, saidretainer assembly comprising: a washer having a central axis anddefining at least a firs aperture in communication with said at leastone fastener bore, said washer further configured to retain said headsof at least two bone engaging fasteners extending through certain onesof said openings in said plate; and a locking fastener for said firstaperture having an elongated shank extending through said aperture andconfigured to engage said fastener bore of said plate, said washer beingmovable along said central axis between a first position whereby said atleast two bone engaging fasteners are insertable into certain ones ofsaid openings and a second position whereby washer retains said at leasttwo bone engaging fasteners in said plate.
 42. The retainer assembly ofclaim 41, wherein said apertures of said washer form slots having alength extending in the direction of the length of the plate.
 43. Theretainer assembly of claim 42, wherein each of said apertures include acountersink portion communication with said slot.
 44. The retainerassembly of claim 42, wherein said countersink portion of at least oneof said apertures is tapered and has a width that increases along thelength of said aperture from a second end to a first end.
 45. A methodfor applying a compressive load to a portion of the spinal column, thespinal column portion including at least a first vertebra and a secondvertebra, the method comprising: engaging a pin to the second vertebra;placing a sleeve over the pin; providing a plate having a lengthextending between a first end and a second end, the plate including anotch on the second end, and a number of openings through the plate;placing the plate on the spinal column portion with the sleeve nested inthe radius of the plate; fixing the first end of the plate to the firstvertebra with bone engaging fasteners extending through the openingspositioned over the first vertebra; removing the sleeve from the pin toform a gap between the pin and the notch; connecting a compression toolto the pin and the plate; and applying a compression load to the spinalcolumn portion with the compression tool until the pin contacts thenotch.
 46. The method according to claim 45, wherein engaging a pin tothe second vertebra includes: providing a template having a guidesurface and a notch; positioning the template on the second vertebrawith the guide surface on an endplate of the second vertebra to locatethe notch on the body of the second vertebra; inserting a pin throughthe notch of the template into the body of the second vertebra; andremoving the template;
 47. The method according to claim 45, furthercomprising providing a plate with holes positioned over the firstvertebra and slots positioned over the second vertebra.
 48. The methodaccording to claim 45, further comprising retaining the bone engagingfasteners in the plate with a retainer assembly.
 49. A method forallowing graft settling in a portion of a spinal column, comprising:providing a plate having a length between a first end and a second endsized to span at least two vertebra, the plate having a pair of holes atthe first end positioned over the first vertebra and a pair of slots atthe second end positioned over the second vertebra; fixing the first endof the plate to the first vertebra with bone engaging fastenersextending through the pair of holes; securing the second end of theplate to the second vertebra with bone engaging fasteners extendingthrough the pair of slots; and translating the bone engaging fastenersin the slots to allow settling of the spinal column portion.
 50. Themethod according to claim 49, further comprising retaining the boneengaging fasteners in the plate with a retainer assembly.
 51. The methodaccording to claim 50, wherein the retainer assembly includes a washerhaving a length substantially corresponding to the length of the plate.